Topic 4B: Diversity And Selection

Question 1

What number of chromosomes do normal body cells have

Answer 1

Diploid (2n)
2 of each chromosomes one from mum and one from dad

Question 2

What do chromosomes pair up in

Answer 2

Homologous pairs

Question 3

How many homologous pairs do humans have

Answer 3

23 pairs and 46 chromosomes

Question 4

What are the 2 types of gametes

Answer 4

Egg and Sperm

Question 5

What number of chromosomes do gametes have

Answer 5

Haploid (n)
Only one copy of each chromosomes

Question 6

What’s the haploid number of chromosomes

Answer 6

23

Question 7

What happens in sexual reproduction

Answer 7

Two gametes join together at fertilisation to form a zygote which divides and develops into a new organism

Question 8

What happens at fertilisation

Answer 8

A haploid sperm fuses with haploid egg, making a cell with the normal diploid number of chromosomes
Half of these chromosomes are from father half from mother
During sexual reproduction any sperm can fertilise any egg, fertilisation is random

Question 9

What does random fertilisation produce

Answer 9

Zygotes with different combinations of chromosomes to both parents
Mixing of genetic material in sexual reproduction increase’s genetic diversity within a species

Question 10

What is meiosis

Answer 10

Type of cell division that takes place in the reproductive organs of multicellular, eukaryotic organisms
Cells that divide by meiosis are diploid to begin with them become haploid

Question 11

What are the 6 steps of meiosis

Answer 11

1) Before meiosis starts the DNA unravels and replicates so there are 2 copies of each chromosomes called chromatids
2) The DNA condenses to from double armed chromosomes each made from 2 sited chromatids they are joined in the middle by a centromere
3) Meiosis I (first division) the chromosomes arrange themselves into homologous pairs
4) These homologous pairs are then separated halving the chromosome number
5) Meiosis II (second division) the pairs of chromatids that make up each chromosome are separated (centromere is divided)
6) Four haploid cells that are genetically different from each other are produced

Question 12

What are the 2 main ways that genetic diversity is created

Answer 12

Crossing over and independent segregation

Question 13

What happens when crossing over occurs

Answer 13

Homologous chromosomes come together twist around each other and bits of the chromosomes swap over
The chromatids still contain the same genes but different combination of the alleles

Question 14

What happens when independent segregation occurs

Answer 14

Each homologous pair of chromosomes in your cells is made up of one from mam and one from dad
When pairs separate in meiosis it’s completely random meaning each cell has a different combination of chromosomes
This ‘shuffling’ creates genetic variation in any potential offspring

Question 15

What is a gene mutation

Answer 15

Involves a change in the DNA base sequence of chromosomes

Question 16

What are the 2 types of gene mutation

Answer 16

Substitution and deletion

Question 17

What is a substitution mutation

Answer 17

One base substituted with another

Question 18

What is a deletion mutation

Answer 18

One base is deleted

Question 19

What are the effects of gene mutations

Answer 19

Degenerate nature of genetic code means that same AA are coded for by more than one DNA triplet
Meaning not all substitution mutations result in a change to the AA sequence of the protein
But deletions always will lead to changes in the AA sequence as it changes the number of bases present and leads to a frame shift

Question 20

What are mutagenic agents

Answer 20

Mutations occur spontaneously but some things can cause an increased rate of mutations these are mutagenic agent

Question 21

Give 2 examples of mutagenic agents

Answer 21

UV light and Ionisation radiation

Question 22

What is a chromosome mutation

Answer 22

When Changes to the number of chromosomes occurs usually due to errors in meiosis

Question 23

What do chromosomes mutations lead to

Answer 23

Inherited conditions

Question 24

Give an example of chromosome mutation and explain it

Answer 24

Chromosome disjunction: Failure for chromosomes to separate properly

Question 25

What is genetic diversity

Answer 25

Number of different alleles in a species or population
A large number of alleles in a population leads to a high genetic diversity

Question 26

Why is a low genetic diversity in a population bad

Answer 26

Might not be able to adapt to change in the environment and the whole population could be wiped out by a single event (e.g diversity)

Question 27

In what 2 ways can genetic diversity be increased by in a population

Answer 27

Mutations in the DNA forming new alleles, some of these can be advantageous whilst others can lead to problems
Different alleles being introduced into a population when individuals from another population migrate into it anD reproduce (this is known as gene flow)

Question 28

What allows for natural selection

Answer 28

Genetic diversity

Question 29

What is a genetic bottle neck

Answer 29

Event that causes a big reduction in the population
This reduces the number of different alleles in the gene pool and so reduces genetic diversity
The survivors reproduce and larger population is created from a few individuals

Question 30

What does the founders effect describe

Answer 30

What happens when just a few organisms from a population start a colony and there’s only a few small number of different alleles in the initial gene pool. The frequency of each allele in the new colony might be very different to that in the original population

Question 31

What can the founders effect occur as a result of

Answer 31

Migration leading to geographical separation

Question 32

What is natural selection

Answer 32

Allele cod’s for a characteristic that increases the chances of an organism serving its frequency in the pop then increases

Question 33

Whats the 5 steps to natural selection

Answer 33

1) Not all individuals are as likely to reproduce as each other (differential reproductive success) a random mutation may occur creating an advantageous allele to be produced which is beneficial
2) meaning they are more likely to survive and reproduce passing allele onto offspring
3) those without it are less likely to survive and causes them to eventually die off leaving only those with beneficial allele
4) so frequency of this allele increases in each generation
5) over generations it leads to evolution as advantageous allele becomes common in the pop

Question 34

What is evolution

Answer 34

Gradual change in species overtime, it has led to the huge diversity of living organisms

Question 35

What are the 3types of adaptation

Answer 35

Behavioural, physiological and anatomical (structural)

Question 36

What are behavioural adaptations

Answer 36

Ways organisms act that increase its chance of survival

Question 37

What are physiological adaptations

Answer 37

Processes inside the body that increase chance of survival

Question 38

What are anatomical adaptations

Answer 38

Structural features of an organisms body that increase chance of survival

Question 39

What are the two types of selection

Answer 39

Stabilising and directional

Question 40

What is directional selection

Answer 40

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce, this could be in response to an environmental change

Question 41

What is stabilising selection

Answer 41

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce, occurring in response to an environmental change and reduces the range of possible characteristics